Field of the Invention
The present invention relates to a toner used in an electrophotographic method, an electrostatic recording method, a magnetic recording method and the like.
Description of the Related Art
With the increasing speed and longer life of an electrophotographic apparatus, a toner needs to have resistance to a physical load.
From the perspective of increasing the resistance of a toner to a physical load, investigation has previously been carried out into hindering an external additive present on the toner surface from becoming embedded in the toner surface. The embedding of an external additive in the toner surface occurs during image formation of a plurality of sheets, for example, causing toner fluidity to deteriorate, charge performance to deteriorate, and the physical adhesive strength to increase. Consequently, developing properties deteriorate, so that image defects occur, density deteriorates, and parts are welded together.
To hinder an external additive from embedding in the toner surface, many attempts have been made that use an external additive having a large particle diameter. WO2013/063291 and Japanese Patent Application Laid-Open No. 2013-92748 discuss using organic-inorganic composite fine particles as an external additive having a large particle diameter.
Investigation by the inventors showed that the addition of the inorganic fine particles having a large particle diameter like those discussed in WO2013/063291 and Japanese Patent Application Laid-Open No. 2013-92748 has an effect on toner low-temperature fixability. It is thought that the increase of the inorganic fine particles having a large particle diameter makes the gaps among the toner particles large, which inhibits toner melding caused by thermal fusion and fixing of the toner to the paper. Further, to cover a certain area of the toner surface with an external additive having a large particle diameter, the volume of the added external additive increases. In this case, the heat capacity as an external additive increases, so that it becomes difficult to supply thermal energy sufficient for the fusing of the toner base particles during fixing. This point is also thought to be a reason for deterioration in low-temperature fixability.
As described above, it is difficult to achieve low-temperature fixability while also maintaining developing properties during image formation of a large number of sheets. The achievement of both of these properties has been a longstanding problem for electrophotographic apparatuses.
Further, since the adhesive strength of the external additive to the toner surface is reduced by the increase in grain size, an external additive having a large particle diameter tends to detach from the toner, which causes the problem that the parts become contaminated by the external additive having a large particle diameter during prolonged use.
Thus, although the addition of an external additive having a large particle diameter is effective as a measure to increase speed and achieve longer life, many problems still remain. Accordingly, further measures are required.